The present invention relates to a magnetic recording and reproducing apparatus, and more particularly to an automatic tracking apparatus for a helical scan type video tape recorder (hereinafter referred to as the "VTR").
FIG. 14 is a diagram illustrating an example of the relationship between the magnetic head width and the track width in a 2-hour mode and an 6-hour mode in a VHS system which is one system utilized by existing home VTRs. In the 6-hour mode, the arrangement is such that the magnetic head width is grater than the track width, the former being 33 .mu.m and the latter 19 .mu.m.
FIG. 15 illustrates an example of the actual measurement of deflection of a video track in the VHS system. Such deflection of the track is caused by mechanical factors such as the machining accuracy of a cylinder around which a video tape is wrapped and unevenness in the tension of the tape around the cylinder, and an S-shaped curve characteristic is displayed. In terms of the effect of the deflection of the track on reproduced signals, since the main cause of the deflection of the track lies in the aforementioned mechanical factors, in many cases no problems are presented when self-recording and reproduction is carried out. In cases other than the self-recording and reproduction, however, a problem arises since a deviation of the track occurs due to the deflection of the track. For this reason, an arrangement is provided in the VHS system such that slant azimuth recording at an azimuth angle of 12.degree. is effected to so as to reduce cross-talk from adjacent tracks. In addition, in the 6-hour mode, the recording track width is set to 1.5-2.0 times the recording track width of 19 82 m so that reproduction of signals will be possible even if some deviation of the track occurs.
FIG. 16 illustrates the relationship between the magnetic head and a recording pattern at the time of recording in the 6-hour mode. As is apparent from the drawing, if recording is carried out with a magnetic head having a head width of W .mu.m 1.5-2 times the recording track width of 19 .mu.m, an overwrite region .times.of W 19 .mu.m occurs. In this region x, low-frequency components and, for video signals, chrominance signals converted in a low-frequency band are apt to be left unerased, a deterioration in picture quality at the time of reproduction.
FIG. 17 illustrates the relationship between the magnetic head and the recording pattern at the time of reproduction in the 6-hour mode. An arrangement is provided such that reproduction is carried out with an .times..mu.m-wide magnetic head as compared to the track width of 19.mu.m so that signals can be read even if some track deviation occurs by making use of an azimuth loss. If reproduction of signals is carried out with such a wide magnetic head, the deviation of the track can be coped with, but there is a problem in that the picture quality is unavoidably deteriorated by that margin due to cross-talk from adjacent tracks with respect to low-frequency signals, down converted chrominance signals, etc. that have low azimuth loss.
In such a conventional VHS system, solutions for the deflection of the track caused mainly by mechanical factors have been provided only through the mechanical accuracy of the magnetic head and the like without providing any electrical automatic tracking control.
Since the conventional magnetic recording and reproducing apparatus is arranged, as described above, there has been the drawback that, in a long-recording/reproducing mode, the deterioration in the picture quality is unavoidable due to the incomplete erasure of low-frequency components at the time of overwrite as well as cross-talk of low-frequency components from adjacent tracks and with a low azimuth loss.